Field of the Invention
The invention relates generally to tractor-trailers and to frames and sub-frames for tractor-trailers. More particularly the invention is directed to a hanger that attaches to the frame of a tractor-trailer and which is used to mount the axle/suspension system to the frame. More specifically, the invention is directed to a hanger that includes a plurality of slotted openings for mounting the hanger to a main member of a frame of a heavy-duty vehicle and at least one circular or oblong-round opening for mounting the hanger to a cross member of the frame of the heavy-duty vehicle. The invention provides the ability to pre-drill the opening patterns on the frame at the trailer original equipment manufacturer, thereby eliminating and/or reducing the need for matched-drilled openings at the time of installation of the hanger on the frame, and also eliminating multiple opening patterns for the hanger, and resulting in decreased cost and complexity of the hanger as well as providing improved adjustment and/or control of hanger spacing, thereby reducing irregular tire wear.
Background Art
Heavy-duty vehicles, such as tractor-trailers or semi-trailers, typically include one or more suspension assemblies that connect the wheel-bearing axles of the vehicle to the frame of the vehicle. Conventional or prior art frame designs were developed before the advent of air suspension systems for trailers. At that time, spring suspension systems were the suspension of choice for trailers. However, the spring suspension system resulted in a relatively rough ride to the cargo and did not equalize loads in all situations, thus creating the need for a frame design with soft ride characteristics and efficient load equalization characteristics. The subsequent development of air suspension systems provided improved ride quality for individual axles of semi-trailers as well as load equalization among multiple axles.
Load equalization is important because the amount of cargo that a trailer may carry is governed by local, state and/or national road and bridge laws, and is dependent on proper load distribution. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as limit the maximum load that can be supported by individual axles. Therefore, the use of air suspension systems that can provide greater load equalization among multiple axles is preferred in order to enable the vehicle to carry as much cargo as is legally allowed.
In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a sub-frame, and the suspension assemblies connect directly to the sub-frame. Sub-frames have been utilized on tractor-trailers for many years. The sub-frame is a box-like structure that is mounted on the underside of the trailer body of the tractor-trailer and one or more axle/suspension systems are suspended from the single sub-frame structure. For those heavy-duty vehicles that support a sub-frame, the sub-frame can be non-movable or movable, the latter being commonly referred to as a slider box, slider sub-frame, slider undercarriage, or secondary slider frame. A trailer having a slider box gains an advantage with respect to laws governing maximum axle loads. Proper placement of the slider box varies individual axle loads or redistributes the trailer loads so that it is within legal limits. Once properly positioned, the slider box is locked in place on the underside of the trailer by a retractable pin mechanism. For the purpose of convenience and clarity, reference herein will be made to frames, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of primary frames, movable sub-frames and non-movable sub-frames.
The axle/suspension system is typically suspended from the main members by a pair of aligned and spaced-apart depending hangers. More specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members, which form the frame of the vehicle. Each beam is pivotally connected at one of its ends to a hanger, which in turn is attached to and depends from a respective one of the main members of the frame of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The end of each beam opposite from its pivotal connection also is connected to a bellows air spring or its equivalent, which in turn is connected to a respective one of the main members.
As set forth above, typical prior art hangers include a rigid connection or mount between the hanger and the underside of the main member of the frame of the vehicle. These rigid connections or mounts typically have consisted of welds and/or bolts. More particularly, a hanger having a generally U-shaped horizontal cross section is welded or bolted to the underside of the main member of the frame of the heavy-duty vehicle and may also be connected and/or mounted to one or more cross members of the frame of the vehicle. Bolting the hanger to the main member and cross member requires the placement of pre-drilled openings in the hanger as well as the main member and the cross member of the frame of the vehicle. However, because of tolerance stacks, the pre-drilled openings in the hanger often do not align properly with the pre-drilled openings in the main members and cross members of the frame. As a result, urging or forcing the hanger openings and the main member and cross member openings to align with one another can create improper hanger spacing, which can in turn lead to misalignment of the axle/suspension system. More specifically, misalignment of the axle/suspension system due to improper hanger spacing results in toe-in or toe-out conditions at the axle spindles of the axle/suspension system. These toe-in or toe-out conditions at the axle spindles can in turn potentially contribute to irregular tire wear. Axle/suspension systems that have less lateral compliance are especially susceptible to toe-in or toe-out conditions at the axle spindles due to improper or offset hanger spacing. Therefore, in order to assure proper hanger spacing, some manufacturers have turned to a process of forming matched-drilled openings in the main members and cross members of the frame based on the pre-drilled openings formed in the hangers. This method of installation assures proper hanger spacing, but can take significant time to complete because it takes significant man hours to form each of the matched-drilled openings in the main members and the cross members of the frame, thereby increasing manufacturing costs. Moreover, because there are many different main member and cross member frame configurations, multiple opening patterns must be formed on the top surface of each hanger to accommodate the various matched-drilled opening placements that occur on the main members and the cross members of the various possible vehicle frames on which a hanger may be ultimately mounted.
In the case where suspensions that self-steer are used, because the wheels/tires steer about a pivot point on the axle, there must be proper clearance for components to prevent wheel/tire rub to the main trailer and suspension components (i.e. trailer frame, suspension beam, suspension air spring, etc.). One method of providing clearance is to space the self-steer suspension frame brackets and beams further inboard than the remaining fixed suspensions on the trailer. This requires the suspension supporting structure of the trailer to accommodate a different spacing for the self-steer suspension only, which no longer matches the remaining fixed suspensions on the trailer, therefore requiring many unique trailer structure components.
Therefore, a need exists in the art for an improved hanger for axle/suspension systems which is free of multiple opening patterns previously required to fit multiple frame configurations, that eliminates and/or reduces the costs associated with matched-drilled openings in the main members and cross members of the frame, and that also allows for improved adjustment and/or control of hanger spacing, thereby avoiding toe-in and toe-out conditions at the axle spindles of the axle/suspension system, thereby reducing the potential for irregular tire wear, and also allowing for improved frame bracket and suspension beam spacing for self-steer suspensions that reduce the required variation in trailer designs that are currently needed to accommodate the self/steer suspensions with the accompanying fixed suspensions, while still maintaining proper clearance for steer components (tires/wheels).
The hanger for axle/suspension systems of the present invention solves the problems associated with prior art bolt-on hangers by including at least one circular or oblong-round opening at the hanger to cross member interface as well as a plurality of slotted openings at the hanger to main member interface. The circular or oblong-round opening at the hanger-to-cross member interface assures proper spacing and/or alignment of the hanger and in turn the axle/suspension system, while the slotted openings at the hanger-to-main member interface provide universal attachment to pre-drilled openings in the main members. The hanger for axle/suspension systems of the present invention allows the openings in the main members and cross members to be entirely or significantly pre-drilled while maintaining adjustability of the hanger and the axle/suspension system for purposes of alignment, thereby eliminating and/or reducing the costs associated with matched-drilled openings in the main members and cross members of the frame at the time of installation of the axle/suspension system to the frame of the vehicle, and also eliminating the need for multiple opening patterns or configurations in the hanger, instead allowing for a single universal opening pattern that allows for connection/mounting of the hanger to vehicles irrespective of frame configuration/opening pattern. The hanger for axle/suspension systems of the present invention also allows for improved adjustment and/or control of hanger spacing, thereby avoiding toe-in and toe-out conditions at the axle spindles of the axle/suspension system, and thereby reducing the potential for irregular tire wear, and also provides improved frame bracket and beam spacing eliminating the need for unique trailer sub-structure so that a trailer sub-structure more closely matched to fixed suspension installations can be utilized.